The present invention relates generally to injection molding materials and processes and, in particular, to a colorization pellet for use in an injection molding process.
Injection molding materials and processes are well known. In an injection molding operation, extruders are utilized for transforming solid materials into a molten mixture for subsequent use in a mold or die via injection. The extruder typically includes an extruder screw disposed therein. Materials that are used for this purpose include a range of plastic materials, as well as various metal or thixotropic materials. The injection molding process includes feeding the solid material in pellet, chip, powder, or flake form to the feed end of the extruder through a hopper or similar device mounted on an opening of a heated cylindrical barrel. The solid material fed into the screw channel is compacted into a solid plug or solid bed and the solid bed melts as it travels down the screw channel. The molten material is then provided to an injection molding machine for forming a part or the like. When the part is formed, defects from the mold known as flow and knit lines are visible in the exterior surface of the part.
It has become more common recently for metallic parts, such as automobile body parts, to be coated on exterior surfaces thereof with paint coatings having a reflective or metallic finish. These paint coatings typically include a plurality of reflective or metallic ingredients disposed therein, such as aluminum flake, coated mica flake, reflective glass beads, reflective glass flake, or holograms. It has also become more common, however, for the exterior of the automobile body to include parts manufactured of injection-molded plastic or other non-metallic material, which present further problems in providing a uniform appearance for the surface of the vehicle. The injection molded parts have been coated in the prior art utilizing a variety of methods including coating the plastic components with a metallic or reflective paint of either low gloss or high gloss. Painting the injection molded part, however, is disadvantageously expensive and time-consuming.
Alternatively, a paint film or a polymer film is applied to the exterior surface of the injection molded part. The paint films or polymer films, however, also have a high associated cost as well as technical challenges including, but not limited to, tooling, draw limitation, graining, trimming, and gloss challenges. Applying the paint film or polymer film to the part is also time-consuming.
A more desirable alternative is to form the part from a plastic material having both the desired color and the desired metallic appearance characteristics so that the part may be installed after being formed without having to be subsequently painted. This alternative, however, has proved to be difficult because the flow and knit lines in the exterior surface of the part are vastly more apparent when the reflective or metallic ingredients, such as those in the metallic paint noted above, are intermixed with the plastic material prior to the extrusion portion of the injection molding operation. The reflective or metallic ingredients disadvantageously tend to orient along the flow and knit lines and do not provide a clean or uniform appearance in the exterior surface of the part.
It is desirable, therefore, to provide a material for use in an injection molding process that will advantageously aid in providing a metallic appearance in the exterior surface of an injection molded part without the need for subsequent painting after the part has been formed.